The subject matter of the present invention relates to hydraulic fracturing simulators adapted for use in the oil and gas industry, and, in particular, to a method and apparatus and program storage device for tracking of fracture fronts associated with a fracture footprint in hydraulic fracturing simulators.
Hydraulic fracturing simulators are routinely used in the oil and gas industry to design hydraulic fracturing (HF) jobs, monitor them in real time, and evaluate the results to improve future HF designs. Most oil wells and many gas wells are hydraulically fractured in order that such wells will become economic and efficient producers of underground deposits of hydrocarbon. There are different classes of HF simulators available in the industry, such as PKN, KGD, Radial, P3D, and PL3D models. These models contain different levels of complexity in their governing equations and each have their own applications. For example, P3D (or pseudo 3D) models are the current industry standard. However, these models have limitations and do not always provide a very accurate result. There is a move towards PL3D (or planar 3D) models in the industry. These Models are deemed to be state of the art and are significantly more accurate than the P3D models, but the PL3D models require complicated mathematical algorithms. There exists a need for improvements to the ‘PL3D’ model of Hydraulic Fracturing (HF) simulators. In this specification, one such improvement to the ‘PL3D’ model of HF simulators will be disclosed. In particular, that improvement to the ‘PL3D’ model lies within the ‘Volume Of Fluid (VOF)’ approach for tracking fracture fronts associated with fracture footprints in hydraulic fracturing simulators. In connection with the aforementioned improvement to the ‘Volume of Fluid’ or ‘VOF’ portion of the ‘PL3D’ model of HF simulators, a key challenge to developing an effective simulator is devising a robust and accurate algorithm to locate the unknown perimeter of the fracture within the fracture plane (which is termed the ‘free boundary’). This specification will disclose two novel Local Volume of Fluid (LVOF) strategies for locating the position of a fracture perimeter during the evolution of that fracture.
In this specification, we will assume that the fluid front matches the fracture front, and that any ‘lag’ between the fluid front and the fracture front is negligible. The VOF approach here disclosed can also, with some alteration, be applied to tracking fronts between different fluids within the fracture, or to tracking the fluid front separately from the fracture front, thereby allowing for the calculation of a ‘lag’ between the fluid front and the fracture front. These possibilities form part of the spirit of this invention.